Method for controlling air flow in a fuel cell power system

ABSTRACT

One aspect of the present disclosure is directed to a fuel cell power system. The system may include one or more fuel cells configured to generate electric power and a compressor configured to supply compressed air to the one or more fuel cells. The system may further include one or more sensors. The sensors may be configured to generate a signal indicative of at least one measured parameter of air flow across the one or more fuel cells. The system may also include a controller in communication with the one or more fuel cells, the compressor, and the sensors. The controller may be configured to determine a desired pressure drop based on at least one calculated parameter, determine a control command for the compressor based on the desired pressure drop, and adjust the control command based on a feedback gain parameter and a feed forward gain parameter.

This application claims the benefit of U.S. Provisional Application No.61/840,862, filed Jun. 28, 2013, which is incorporated herein byreference.

The present disclosure relates to a fuel cell power system. In someembodiments, the fuel cell power system described herein includes acontroller configured to control air flow to one or more fuel cells ofthe fuel cell power system.

Fuel cell power systems have been proposed as a clean, efficient, andenvironmentally responsible power source for both stationary andautomotive applications. A fuel cell power system can include a fuelstack having one or more fuel cells for generating electric power. Inparticular, each fuel cell can include an anode in an anode compartment,a cathode in a cathode compartment, and an electrolyte that allowscharges to move between the anode and cathode. In some examples, a flowof fuel is supplied to the anode, and a flow of oxygen containing gas(e.g., air) is fed to the cathode. The fuel can be catalyticallydisassociated in the anode to generate free protons and electrons. Theprotons can pass through the electrolyte to the cathode and react withthe oxygen and the electrons in the cathode to generate water. Theelectrons can be drawn from the anode to the cathode through an electricload circuit, producing electricity.

The fuel cell stack typically receives oxygen for the cathode fromcharged air provided by an air compressor. In certain fuel cell powersystems, a controller may be provided for controlling the air flow ratethrough the fuel cell stack to vary the electrical output. Where anadjustment in the electrical output is required, the controller may beconfigured to send a command signal to the air compressor to change theair flow rate across through the fuel cell stack. The controller mayalso measure the air flow rate by measuring a pressure drop across thefuel cell stack and determine a difference between the measured pressuredrop and a desired pressure drop across the fuel cell stack. Thecontroller may then be configured to minimize any difference between themeasured air flow rate and the desired air flow rate by adjusting thespeed of the air compressor.

In some circumstances, the controller may be required to quickly adjustthe speed of the air compressor in response to fluctuations in thedemand for electricity. The dynamic response may result in unwantednoise in the signal from pressure sensors measuring the actual pressuredrop across the fuel cell stack, which may then reflect in the commandsignal to the motor of the air compressor. Such signals may causeexcessive revving of the air compressor generating an undesirable sound.Further, such signals may cause a shortage in compressor lifetime.

In consideration of the aforementioned circumstances, the presentdisclosure provides a fuel cell power system having a controllerconfigured to control air flow to one or more fuel cells of the fuelcell power system. The controller may be configured adjust the commandsignal to the compressor to provide a fast dynamic response whilereducing the overall noise of the air compressor.

One aspect of the present disclosure is directed to a fuel cell powersystem. The fuel cell power system may include one or more fuel cellsconfigured to generate electric power and a compressor configured tosupply compressed air to the one or more fuel cells. The fuel cell powersystem may further include one or more sensors associated with the oneor more fuel cells. The one or more sensors may be configured togenerate a signal indicative of at least one measured parameter of airflow across the one or more fuel cells. The fuel cell power system mayalso include a controller in communication with the one or more fuelcells, the compressor, and the one or more sensors. The controller maybe configured to determine a desired pressure drop across the one ormore fuel cells based on at least one calculated parameter, determine acontrol command for the compressor based on the desired pressure drop,and adjust the control command based on a feedback gain parameter and afeed forward gain parameter.

Another aspect of the present disclosure is directed to a method forcontrolling air flow in one or more fuel cells of a fuel cell powersystem. The method may include supplying a pressurized air stream from acompressor to the one or more fuel cells. The method may further includedetermining a desired pressure drop across the one or more fuel cellsbased on at least one calculated parameter, determining a controlcommand for a compressor based on the desired pressure drop, andadjusting the control command based on a feedback gain parameter and afeedforward gain parameter.

Additional objects and advantages of the present disclosure will be setforth in part in the description which follows, and in part will beobvious from the description, or may be learned by practice of thepresent disclosure. The objects and advantages of the present disclosurewill be realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the systems and methods, as claimed.

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the disclosure andtogether with the description, serve to explain the principles of thedisclosure. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 1 is a block diagram of a fuel cell power system, according to anexemplary disclosed embodiment.

FIG. 2 is a flow chart of a method of controlling air flow to a fuelcell stack in a fuel cell power system, according to an exemplarydisclosed embodiment.

FIG. 3 is a graph comparing the desired pressure drop and the measuredpressure drop in response to a stepped change in demand by an electricload.

FIG. 4 is a graph illustrating the duty cycle of a motor of an aircompressor in response to a stepped change in demand by an electricload.

Reference will now be made in detail to the present exemplaryembodiments of the disclosure, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

FIG. 1 illustrates an exemplary fuel cell power system 10 and relatedcomponents. The exemplary fuel cell power system 10 may be configured togenerate electric power for automotive, portable, and industrialapplications. In the exemplary embodiment, the components of fuel cellpower system 10 include a fuel cell stack 12, an air compressor 24, anda fuel supply 26.

Fuel cell stack 12 may include one or more fuel cells. The one or morefuel cells may be connected electrically in series and/or in parallel ina manner commonly known in the art. A schematic representation of fuelcell stack 12 is shown in FIG. 1, with the anode side of fuel cell stack12 designated with the reference numeral 22 and the cathode side of fuelcell stack 12 being designated with reference numeral 20. The fuel cellstack 12 further includes an anode inlet 19, an anode outlet 21, acathode inlet 34, and a cathode outlet 42.

As shown in FIG. 1, the anode inlet 21 is in fluid communication withfuel supply 26 and the cathode inlet 34 is in fluid communication withcompressor 24. Compressor 24 may be any known compressor in the art.Compressor 24 is configured to provide charged air to cathode inlet 34of the fuel cell stack 12 via line 32. The air may be drawn from theatmosphere, typically though a filter (not shown) to compressor 24.Compressor 24 may be electrically or mechanically coupled to motor 28 todrive compressor 24 at a speed sufficient to provide a desired quantityof charged air to cathode side 20.

As explained above, a chemical reaction may occur in fuel cell stack 12to produce electric power. In particular, the fuel supplied to anodeside 22 may be catalytically disassociated in anode side 22 to generatefree protons and electrons. The protons may pass through an electrolyte(not shown) to cathode side 20 and react with the oxygen and theelectrons in the cathodes to generate water. The electrons can be drawnfrom the anodes to the cathodes outputting a current to electric load14. Excess fuel may be removed from fuel cell stack 12 via anode outlet21, and excess air may be removed from fuel cell stack 12 via cathodeoutlet 42.

Fuel cell power system 10 may include components that together areconfigured to control air flow through fuel cell stack 12, by regulatingthe speed of compressor 24. In particular, fuel cell power system 10 mayinclude one or more sensors and a controller 18 in communication withthe fuel cell stack 12, the one or more sensors, and motor 28 drivingcompressor 24. Each of the one or more sensors may be configured todetect and/or measure at least one operational aspect associated withfuel cell power system 10. Based on the inputs from the fuel cell stack12 and the one or more sensors, controller 18 may regulate air flowthrough the fuel cell stack by varying the speed of compressor 24.

As shown in FIG. 1, the one or more sensors include a cathode inlet airpressure sensor 36 positioned adjacent cathode inlet 34 and a cathodeoutlet air pressure sensor 44 positioned adjacent cathode outlet 42. Thecathode inlet pressure sensor 36 and the cathode outlet pressure sensor44 may be pressure transducers configured to measure the air pressure atcathode inlet 34 and air pressure at cathode outlet 42 of fuel cellstack 12, respectively. It will be understood that other sensors may beemployed to directly or indirectly measure the air-flow through fuelcell stack 12. The cathode inlet pressure sensor 36 is in communicationwith controller 18 via line 40 and the cathode outlet pressure sensor 44is in communication with controller 18 via line 48. Each of thesesensors may generate signals directed to controller 18 via lines 40 and48 for further processing.

Controller 18 may embody, for example, one or more generalmicroprocessors capable of controlling numerous functions of fuel cellpower system 10. Controller 18 may include a memory, a secondary storagedevice, a processor (e.g., a CPU), or any other components for executingprograms to perform the disclosed functions of fuel cell power system10. Various other circuits may be associated with controller 18, such aspower supply circuitry, signal conditioning circuitry, data acquisitioncircuitry, signal output circuitry, signal amplification circuitry, andother types of circuitry known in the art.

Controller 18 may be configured to initiate, monitor, and adjust thespeed of compressor 24. In particular, controller 18 may be configuredto receive inputs from sensors 36, 44. In addition, controller 18 may bein communication with fuel cell stack 12 via electric load 14.Controller 18 may be configured to receive a signal via line 16indicative of a power demand by electric load 14. In response tofluctuations in the demand by electric load 14, controller 18 may beconfigured to send a command signal to motor 28 of compressor 24 toadjust the speed of compressor 24. In this manner, controller 18 mayregulate air flow through the fuel cell stack, based on the speed ofcompressor 24.

FIG. 2 illustrates an exemplary method 50 for controlling air flowconsistent with this disclosure. As shown in the flowchart of FIG. 2,the first step in the method may include sending a control command tomotor 28 (step 52) to set compressor 24 at a speed sufficient to providea desired quantity of charged air to cathode side 20 of fuel cell stack12.

As fuel cell stack 12 is generating electric power, controller 18 maycontinuously receive a signal from electric load (step 54). The signalfrom the electric load may be indicative of the power dissipated byelectric load 14. Controller 18, based on the power dissipated byelectric load 14, may then calculate a current drain value (step 55).The current drain value may be calculated using one or more equationsstored in memory, and/or may be determined by, for example, referencingthe configuration of fuel cell stack 12 and the fuel cell stack voltagewith one or more lookup tables stored in memory. It is contemplated thatin some embodiments the current drain value may be directly measured by,for example, a current sensor. Controller 18 may then determine adesired pressure drop across fuel cell stack 12 to generate the desiredpower output (step 56). The desired pressure drop may correspond to thedesired air flow rate across fuel cell stack 12. The desired poweroutput may correspond to the power demand by electric load 14. As withstep 55, determination of the desired pressure drop may be made usingone or more equations stored in memory and/or by using one or morelookup tables stored in memory.

Controller 18 may also receive signals indicative of the actual airpressure at cathode inlet 34 and actual air pressure at cathode outlet42 based on the inlet air pressure sensor 36 and outlet air pressuresensor 44, respectively. Controller 18 may, based on the input received,then determine a measured pressure drop across the fuel cell stack 12(step 58). It will be understood that the measured pressure drop maycorrespond to the actual airflow rate across fuel cell stack 12.Controller 18 may compare the measured pressure drop to the desiredpressure drop to determine if there is an error between the desired andactual pressure drop values (step 60), and thus determine changes in theair flow across fuel cell stack 12. The error may reflect, for example,a change in the power demand by electric load 14.

Controller 18, in the disclosed embodiment, is a PID (ProportionalIntegral Derivative) type of controller, which utilizes different gainparameters to adjust an amount by which the displacement of motor 28 isvaried via a control command signal. In general, the PID controllerdetermines a feedback gain parameter (step 62), which can be computedfrom proportional, integrative, or derivative actions. It will beunderstood, however, that controller 18 can be any other knowncontroller configured to utilize different gain parameters to adjust theamount by which the displacement of motor 28 is varied. For example, incertain embodiments, controller 18 can be a feed-back controller or anyother known controller suitable for a feedback control loop. Inadditional and/or alternative embodiments, controller 18 can include afeed-forward controller or any other known controller suitable for afeed forward control loop.

The feedback gain parameter, in the disclosed application, generallycorresponds with an amount of change that should be implemented based onan amount of error measured between desired and actual pressure dropvalues. Determination of the feedback gain parameter may be made usingone or more equations stored in memory. Controller 18 may generate asignal that reflects the required air-flow rate based on the feedbackgain parameter.

Controller 18 may further determine a feed forward gain parameter (step64). The feed forward gain parameter, in the disclosed application, maycorrespond to a percentage of the maximum velocity of compressor 24(e.g., duty) required to achieve the desired pressure drop. The feedforward gain parameter may be determined based on a magnitude of thedesired pressure drop. Controller 18 may be configured to generate asignal that reflects the required air flow based on the feed forwardgain parameter.

Controller 18 may then sum the signal based on the feedback gainparameter and the signal based on the feed forward gain parameter. Othercombining operations may be used as well. The control command may beadjusted to reflect the combined signal (step 66). The displacement ofmotor 28 maybe varied based on the adjusted control command signalwhich, in turn, may adjust the speed of compressor 24 (step 68). Sincethe signal effectively supplied to compressor 24 is a combination of thesignal based on the feedback gain parameter and the signal based on thefeed forward gain parameter, compressor 24 will remain stable without,for example, the excessive winding characteristics of the prior artsystems. FIGS. 3 and 4 reflect this principal.

FIG. 3 is a graph that plots a desired pressure drop 70 in response to astepped change in the demand by electric load 14. Line 72 reflects themeasured pressure drop adjusted based on only the feedback gainparameter and line 74 reflects the measured pressure drop adjusted basedon a combination of the feedback gain parameter and the feed forwardgain parameter. As shown in FIG. 3, adjustments in the air flow ratebased on a combination of the feedback gain parameter and the feedforward gain parameter reflect less noise in the measured pressure dropsignal as compared to the measured pressure drop adjusted based on onlythe feedback gain parameter.

FIG. 4 plots the command signal to motor 28 of compressor 24 based onthe feedback gain parameter only and the signal to motor 28 based on thecombination of the feedback and feed forward gain parameters. As shownin FIG. 4, the combination of the signal based on the feedback and feedforward gain parameters is stable without, for example, the excessivewindings present in the signal to motor 28 based on only the feedbackgain parameter.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A fuel cell power system comprising: one or morefuel cells configured to generate electric power; a compressorconfigured to supply compressed air to the one or more fuel cells; oneor more sensors associated with the one or more fuel cells andconfigured to generate a signal indicative of at least one measuredparameter of air flow across the one or more fuel cells; and acontroller in communication with the one or more fuel cells, thecompressor, and the one or more sensors, the controller being configuredto: determine a desired pressure drop across the one or more fuel cellsbased on at least one calculated parameter; determine a control commandfor the compressor based on the desired pressure drop; and adjust thecontrol command based on a feedback gain parameter and a feed forwardgain parameter.
 2. The fuel cell power system of claim 1, wherein thecontroller is further configured to determine the feed forward gainparameter based on the desired pressure drop.
 3. The fuel cell powersystem of claim 1, wherein the feed forward gain parameter is calculatedbased on a magnitude of the desired pressure drop.
 4. The fuel cellpower system of claim 1, wherein the one or more sensors are configuredto measure pressure of the compressed air at a cathode input of the oneor more fuel cells and at a cathode output of the one or more fuelcells.
 5. The fuel cell power system of claim 4, wherein the one or moresensors are configured to determine a measured pressure drop in airflowing across the one or more fuel cells based on a difference betweenthe pressure at the cathode input of the one or more fuel cells and thecathode output of the one or more fuel cells.
 6. The fuel cell powersystem of claim 5, wherein the controller is further configured todetermine the feedback gain parameter based on a difference between themeasured pressure drop and the desired pressure drop.
 7. The fuel cellpower system of claim 1, wherein the one or more sensors are pressuretransducers.
 8. The fuel cell power system of claim 1, wherein the atleast one calculated parameter is a value approximating a current outputto an electrical load.
 9. The fuel cell power system of claim 1, whereinthe compressor has variable speed that is adjustable in response to thecontrol command.
 10. The fuel cell power system of claim 1, wherein thecontrol command is directed to a motor of the air compressor.
 11. Thefuel cell power system of claim 1, wherein each of the one or more fuelcells include an anode and a cathode, wherein the compressor isconfigured to provide compressed air to the cathode of each of the oneor more fuel cells, wherein hydrogen gas is provided to the anode ofeach of the one or more fuel cells, and wherein the compressed air ofthe cathodes and the hydrogen gas of the anodes react to produce anelectrical power output.
 12. A method for controlling air flow in one ormore fuel cells of a fuel cell power system, the method comprising:supplying a pressurized air stream from a compressor to the one or morefuel cells; determining a desired pressure drop across the one or morefuel cells based on at least one calculated parameter; determining acontrol command for a compressor based on the desired pressure drop; andadjusting the control command based on a feedback gain parameter and afeedforward gain parameter.
 13. The method of claim 12, furtherincluding detecting a measured pressure drop in air flowing across theone or more fuel cells.
 14. The method of claim 12, further includingdetermining the feedback gain parameter based on a difference betweenthe measured pressure drop and the desired pressure drop.
 15. The methodof claim 12, further including determining the feedforward gainparameter based on the desired pressure drop.
 16. The method of claim12, wherein the feedforward parameter is calculated based on a magnitudeof the desired pressure drop.
 17. The method of claim 12, furtherincluding adjusting a speed of the compressor in response to the controlcommand.
 18. The method of claim 12, wherein the fuel cell power systemfurther includes an electrical load, and wherein the at least oneparameter is a value approximating current output to the electricalload.
 19. The fuel cell power system of claim 1, further including oneor more sensors to measure airflow across the cathode, and wherein thecontroller is configured to determine the feedback gain parameter basedon the measured airflow.
 20. The method of claim 12, further includingmeasuring airflow across the cathode, and determining the feedback gainparameter based on the measured airflow.